Heat treatment of loaded conductors



.hme i7, 193%, G. w. ELMEN ,763,884

HEAT TREATMENT OF LOADED CONDUCTORS Filed May 29, 1926 Patented June 17, i930 narran STATES PATENT ori-ica GUSTAB' W. EL'MEN, OF LENIA, NEW JERSEY, ASSIGNOR TO WESTERN ELECTRIC COH- PANY, INCORPORATED, OF NEW YORK, N. Y., A CORPORATION OF NEW YORK HEAT TREATMENT OF LOADED CONDUCTORS Application led May 29,

tor. Heretofore the material employed for this purpose has been iron, but recently certain allows consisting chiefly of nickel and iron have been developed which have a much 4 higher permeability than` iron at low magnetizing forces such as are encountered in signalingsysteins. Alloys having these desirable characteristics are disclosed in appli- `taiit"s Patent No. 1',586,884, granted June 1, 1926, upon applicatiom'Serial No. 473,877,

and copending application, Serial No. 48,188,

'filed August V5, 1925. The use of these alloys,

for the purpose of loading submarine cables is disclosed in the patent to Buckley 1,586,874,

granted upon the application Serial No.

3@ 492,725, filed August 16, 1921. As pointed out iii that patent it has been found that the permeability of certain oi these nickel iron alloys is decreased when the material is subjected to strain and for this reason it has been @found desirable to heat-treat the magnetic material after it has been applied to the conductor in order to attain the highest per.- nieability.- Even when-the loading material is treated ater being applied to the conducio tor, strains may be set up in the material during heating and cooling. It has been sag-1 gested that these strains may be due to the une ual expansion and contraction of' 'the con uctor and loading material for it is evident that the thin layer of loading material surrounding the copper conductor must co'ol first, thereby contracting onto the copper conductor and tending to cause sticking or alloying of the two metals under the inuence of pressure and heat so that when the copper 192s.' seriai No. 112,637.

conductor subsequently contracts upon cooling, the loading material will be drawn with it setting up strains in the alloy. These strains, whatever their cause, result in a reduction in the permeability of the material and should therefore be avoided even though the reduction is small. This disadvantage is particularly objectionable in those alloys in which high permeability is developed by -a rapid cooling of the material which causes a more rapid contracting of the outer layer of loading material, but this e'ect may also be noted in other materials in which a slower rate of cooling is employed.

In accordance with the present invention a loaded conductor is subjected to a heat treatment consisting of heating the loaded conductor and cooling slowly to room temperature so that the whole conductor is cooled at such a rate that the deleterious effect of strains inthe loading material is obviated. The desired rate of cooling in each case is dependent upon the composition and characteristics of the particular loading material, but should be such as to develop the highest permeability 'in the alloy and at the same time produce the least reduction in permeabilit due to strains set up in the material. In this respect the rate of cooling should eect a com romise between two of the factors which a ect the permeability of the material or," in other words, the rate of cooling should be such that the deleterious effects, due to strains set up in the material, are so far reducedas to more than compensate for any decrease in permeability due tothe rate of cooling of the alloy, as compared with the rate roducing the maximum permeability possi le in the material when not strained.

Thel invention will be more fully understood by referencel to the drawing in which Figf is a erspective View of a loaded conductorand ig. 2 is a view in crosssection pf one type of furnace which may be used in carrying out the invention; i.

Iny a typical embodiment of the invention there'is provided a composite conductor consisting of a central conductor 4 and a plurality of conductinghstrands 5 surrounding the central core. e conductor is loade to a temperatureabove the magnetic transiwith magnetic tape 6 vand subjected to a 4heat treatment which comprises heating the alloy tion point andy cooling slowly. This temerature is preferably about 900 C. and the i Beating and cooling'processes are continuous,

`being carried out vbypassing' the loaded conductor througha furnace such as that shown f f in -Fi 2. As illustrated the furnace consists of'a c amber 7 heated to approximately 900 C. through which' the 'conductor -is passed. lFrom thence it is passed through a series of three heatingy chambersr 8, 9 and'10 maintained at progressively lower temperatures' of about 700"4 C., 500 C. and 300 C. re-

.Y sectively. `The furnace andthe heating long and the .conductor was moved at the ratel ambers in one instance were each two feet of 15/2 foot 'per minute. This corresponds to a rate of cooling of about degrees. centigrade per minute which is slow as compared with the rateljof cooling in air. rlhe initial permeability of a loading material contain- `ing chromium, nickel, and iron inthe pro- Y portions of 3% chromium, 7 81/2% nickel, andl c the balance iron was found to be'2630 when conductor was cooled comparatively rapidly l foot per minute', the permeability was found terial to be used should be determined by l "to be '2200 indicating that the slower rate of coolin l,was of advantage over a more rapid rate o vcooling and of considerableadvantage overvthe rapid rateof coolin in air. Moreover, further tests on this al oy indil 'cate thatthepermeability of the material is ordinarily increased by a rapid rate of cool-v ing..f'

y ii-:`,ror' course, evident that the rate y*of cooling may be slower than that employed in the examfile cited and if the particular alloy employe it "may be desirable to increase the rate o 50? C.y per minute.

is" one which should be rapidlyv 'cooled in-order to obtain alhigh permeability? steps in the manufacture of a cable or the process may be carried out by itself.

What is claimed is: f

1. TheamethodA of increasing the ermeability of an alloyconsistin chieiiy o nickel and iron ap lied to a con uctor as loading 'materiah w ich ymethod comprises heating said loaded conductor' to approximately 900o C. and subsequently cooling the same by pass-A ing said conductor continuously through a plurality of heated chambers maintained at progressivelyv lower temperatures, so as to cool said loaded conductor at a 2. The method of heat-treating. a conductor continuously loaded with a magnetic material the characteristics of which are sensitive to strain whichcomprises subjectin the loaded structureto a temperature o the order of 900 C. and-.thereafter lowering the temperature ofthe-'structure' at a'rate of the order of 50"' C. per minute ,in such a manner that the conductor andl thevloading material cool together withoutvv either vsetting up strains in the other.

3.,'Ihe method of continuous heat treatment of a conductory loaded throughoutits length with a magnetic material'the charactristics ofwhich are sensitive to-strain comprisinglpassing the loaded conductor through a first eated zone to raise it to a temperature of the order of 900 C. and through-,successive zones of lower temperature to permit it to `co ol at a rate ofthe order .of,50 C, per minute Wherebythe conductor and the .loading materialhave time to cool togetherl without: either setting up' strains in the'other.

In vwitnesls pvwheref, Iiiereunto. subscribe myname t is 28th. a `o May A. D. 1926..

cooling. Moreover, the coefficient-'of expan` Y sion' for various materials differs consider- '1 ably and for this reason the amount of stickmg or strain `may be greater in one case than in another requirin that the rate of cooling l l y be varied in accor ance therewith. In any case the optimum rate of cooling for the niapcriment in orderto attain theihighest per` meabi'lity in the material after heat treatin the-same on the conductor. If a heating van cooling arran ment such as that describedA i above should employed, the length fof the furnace or of any of the heating'chambers may be chan ed and thev temperature of the various cham ers may be altered as desired.

It maybe desired to employ the method as a continuous vprocess in connection with otherrate of about f 

